I reccomend going to your local store and using one of their charging cables to see if the issue is with your nook, or your nook charger. If it is a charger issue, you can replace that pretty easily (usb cords are cheaper online than the whole charging kit in the store), and if the problem is nook based, you'll be in the right place for further assistance. May need a fallback or a hard reset, so make sure you have the email address and password associated with your account as well as anything you have sideloaded backed up on your home computer. Good Luck!
I actually had this happen to me too. The battery charging icon in the notification bar continued to show that my NC was charging after I had unplugged it. I fully turned off my NC and restarted it and then it was fine and has not happened since. I have seen this occur with demo NC's in the store too.